kustomize

kustomize lets you customize raw, template-free YAML files for multiple purposes, leaving the original YAML untouched and usable as is.

kustomize targets kubernetes; it understands and can patch kubernetes style API objects. It's like make, in that what it does is declared in a file, and it's like sed, in that it emits edited text.

This tool is sponsored by sig-cli (KEP).

kubectl integration

To find the kustomize version embedded in recent versions of kubectl, run kubectl version:

> kubectl version --short --client
Client Version: v1.26.0
Kustomize Version: v4.5.7

The kustomize build flow at v2.0.3 was added to kubectl v1.14. The kustomize flow in kubectl remained frozen at v2.0.3 until kubectl v1.21, which updated it to v4.0.5. It will be updated on a regular basis going forward, and such updates will be reflected in the Kubernetes release notes.

Kubectl version	Kustomize version
< v1.14	n/a
v1.14-v1.20	v2.0.3
v1.21	v4.0.5
v1.22	v4.2.0

For examples and guides for using the kubectl integration please see the kubernetes documentation.

Usage

1) Make a kustomization file

In some directory containing your YAML resource files (deployments, services, configmaps, etc.), create a kustomization file.

This file should declare those resources, and any customization to apply to them, e.g. add a common label.

File structure:

~/someApp
├── deployment.yaml
├── kustomization.yaml
└── service.yaml

The resources in this directory could be a fork of someone else's configuration. If so, you can easily rebase from the source material to capture improvements, because you don't modify the resources directly.

Generate customized YAML with:

kustomize build ~/someApp

The YAML can be directly applied to a cluster:

kustomize build ~/someApp | kubectl apply -f -

2) Create variants using overlays

Manage traditional variants of a configuration - like development, staging and production - using overlays that modify a common base.

File structure:

~/someApp
├── base
│   ├── deployment.yaml
│   ├── kustomization.yaml
│   └── service.yaml
└── overlays
    ├── development
    │   ├── cpu_count.yaml
    │   ├── kustomization.yaml
    │   └── replica_count.yaml
    └── production
        ├── cpu_count.yaml
        ├── kustomization.yaml
        └── replica_count.yaml

Take the work from step (1) above, move it into a someApp subdirectory called base, then place overlays in a sibling directory.

An overlay is just another kustomization, referring to the base, and referring to patches to apply to that base.

This arrangement makes it easy to manage your configuration with git. The base could have files from an upstream repository managed by someone else. The overlays could be in a repository you own. Arranging the repo clones as siblings on disk avoids the need for git submodules (though that works fine, if you are a submodule fan).

Generate YAML with

kustomize build ~/someApp/overlays/production

The YAML can be directly applied to a cluster:

kustomize build ~/someApp/overlays/production | kubectl apply -f -

Community

Code of conduct

Participation in the Kubernetes community is governed by the Kubernetes Code of Conduct.